Summer is a time for postcards. But these were not your typical fun-in-the-sun dispatches from exotic beaches.

Rep. Rodney Frelinghuysen (R-11th Dist.) received a cold blue stack on Wednesday, hand-delivered to his Morristown office by local activists.

“Not One More,” read the 3,300 cards, echoing the chilling demand of a grieving father whose son, a college student at the University of California, Santa Barbara, was shot dead by a mass killer over the Memorial Day weekend.

Each card carries an anguished statement from Richard Martinez, whose son Christopher, 20, was among six people slain by 22-year-old Elliot Rodger, who legally purchased guns despite a history of mental problems. Every card also bears the name of a constituent who registered online.

The campaign anticipates distributing more than 6 million of these postcards to elected officials nationwide.

“It’s to show our congressman we are tired of the gun violence. It’s getting a little too close for comfort,” said Florham Park resident Amy McNulty. She said her son a friend of Brendan Tevlin, a 19-year-old graduate of Seton Hall Prep who was shot and killed last week in West Orange.

Another participant in Wednesday’s postcard event, Susan Pritchard of West Caldwell, also understands the Martinez family’s pain. Susan’s son, Danielle Pritchard, was shot dead while working at a Verona gas station in 2009. He was 29.

“Hopefully, people will understand that we’re not trying to take away guns,” Susan said. “We just want stricter background checks.”

Congressman Frelinghuysen met privately with organizers after the demonstration. Through a spokesman, he issued a statement:

“I was pleased to meet with the local leaders of Moms Demand Action and Everytown for Gun Safety earlier today and to take delivery of the post cards they had collected. We had a good conversation and I appreciate their taking the time to share their views with me.”